Browning, Thomas J. , Rapp, Insa, Schlosser, Christian , Gledhill, Martha , Achterberg, Eric P. , Bracher, Astrid and Le Moigne, Frederic A. C. (2018) Influence of iron, cobalt, and vitamin B12 supply on phytoplankton growth in the tropical East Pacific during the 2015 El Niño. Geophysical Research Letters, 45 (12). pp. 6150-6159. DOI 10.1029/2018GL077972.

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Abstract

Iron (Fe), cobalt (Co), and vitamin B12 addition experiments were performed in the eastern Equatorial Pacific/Peruvian upwelling zone during the 2015 El Niño event. Near the Peruvian coastline, apparent photosystem II photochemical efficiencies (Fv/Fm) were unchanged by nutrient addition and chlorophyll‐a tripled in untreated controls over two days, indicating nutrient replete conditions. Conversely, Fe amendment further away from the coastline in the high nitrate, low Fe zone significantly increased Fv/Fm and chlorophyll‐a concentrations. Mean chlorophyll‐a was further enhanced following supply of Fe+Co and Fe+B12 relative to Fe alone, but this was not statistically significant; further offshore, reported Co depletion relative to Fe could enhance responses. The persistence of Fe limitation in this system under a developing El Niño, as previously demonstrated under non‐El Niño conditions, suggests that diminished upwelled Fe is likely an important factor driving reductions in offshore phytoplankton productivity during these events.

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